U.S. Pat. No. 3,836,712 to P. G. Kornreich and S. T. Kowel discloses a pictorial information digital simulation technique that operates on the irradiance distribution of an image as a function of position. The device is a real time sensor which optimally determines the one-dimensional Fourier transform of a two-dimensional image, using the photo-acoustic surface properties of physical materials. This incoherent light device outputs to a single pair of terminals a set of time sequential voltages, each of which indicates the phase and amplitude of a particular Fourier component. The resulting ac output represents a bandwidth limited, undirectional Fourier transform of the image. This procedure creates a one-dimensional function out of the original two-dimensional image.
The present invention involves a somewhat analogous technique of Fourier transforming an image, using a digital technique which looks at the image irradiance as a function of position. The detected image is digitized either directly on a detector, or subsequently through an analog-to-digital converter, to produce an n.times.n pixel matrix whose elements correspond to the irradiance of the image at a particular pixel position. A large amount of data is quickly reduced to a single pair of n-component vectors by summing along the rows or columns of the pixel matrix. A one-dimensional Fourier transform representation of the image can be obtained from either of the two vectors. An n.sup.2 component pixel matrix is reduced to a pair of n component image vectors. The number of pixels is effectively reduced from n.sup.2 to 2n. In an illustrative case a 512.times.512 matrix will be reduced from over a quarter million elements to 1024 elements, a reduction in data of about 99%. The signal-to-noise ratio of each component in the image vectors is increased approximately by a factor of .sqroot.n. Data storage requirements are reduced significantly by scanning the image line by line and repeatedly adding to a single storage block of n words. Computation times are reduced as compared with operations on a two-dimensional Fourier transform image which may require over a million complex operations that can take a digital computer several minutes to complete, depending on the speed and memory capacity of the computer.